"88% of rail respondents deem government support for the provision of rail infrastructure 'essential'.
Improving the capacity on existing lines is regarded as the most urgent infrastructure need."
The main reason for the lack of investment in infrastructure is because the profits made from rail fares are paid to the shareholders of the privatised train companies. You will not get significant infrastructure spending on the railways unless they are re-nationalised. Currently privatised rail services are subsidised by the taxpayer by about 5 times as much as BR was.
http://www.theguardian.com/commentisfree/2013/aug/13/rail-fares-passengers-renationalisation
Off-point, but some interesting stuff here:
http://www.passengerfocus.org.uk/key-issues/future-of-transport/nine-future-stories